Computation of lightning induced voltages on telecommunication subscriber lines

Abstract

The electric and magnetic fields produced by a lightning stroke in the vicinity of a telecommunication line can illuminate the line and it can acquire induced overvoltages which may be detrimental to the equipments connected to the telecommunication line. The magnitude and waveshape of the electromagnetic fields produced by lightning as well as the induced voltage on telecommunication line are influenced by the finite conductivity of the ground. In this paper, the induced transient voltages on an overhead telecommunication subscriber line due to a nearby lightning stroke to the ground are computed. From the results it is seen that the induced voltage is bipolar for all the observation points except at the line midpoint for the lightning striking point location chosen in this study. It is also observed that the finite ground conductivity decreases the magnitude of the induced voltage at the line terminations where as it increases the induced voltage as the line mid point is approached. The results obtained in this study will be useful in evolving a suitable lightning protection scheme for the rural telephone exchanges which are interconnected using overhead lines instead of underground cables as in the case of urban exchanges. At the same time these rural telephone exchanges have become more vulnerable to transient overvoltages as they are being converted into digital ones with their susceptibility levels for transient overvoltages being much lower than the old electromechanical exchanges. � 2001 Convenor.